Due to the ever improved efficiency of motor vehicle engines or due to the use of electric propulsion for motor vehicles, increasingly less waste heat is available for the comfortable heating of the vehicle cabins. Hence, supplemental heating systems are needed, which support the heating of the interior of the vehicle and thereby increase the comfort of the passengers.
Various supplemental heating systems for vehicle air conditioning systems are known from the prior art.
Besides electrical supplemental heating systems, refrigerant-based heat pumps are also being used. Here, besides the classical heat pump circuits which ensure the heating function by switching the flows of refrigerant in the refrigerant circuit, compact heat pump systems are also known, in which the functions of heating, cooling, and dehumidifying as well as the creation of any given mixed temperature can be realized by means of a standard refrigerant circuit thanks to specific interconnections at the air side of the system.
Compact motor vehicle air conditioning systems of the latter kind are known from DE 10 2012 108 891 A1 and DE 10 2011 052 752 A1, in which a warm air flow from the condenser and a cold air flow from the evaporator of the refrigerant circuit are mixed in accordance with the required expelled air temperature of the vehicle air conditioning system. The mixed air is taken through an air duct into the vehicle cabin. Thanks to an air distribution system arranged in the cabin with various outlet control elements, the air is taken to the corresponding air outlets, such as the defrost, ventilation, and foot space outlet, into the vehicle. Excess air is blown into the surroundings by additional outlets from the compact air conditioning system. These devices already have an increased efficiency and less complexity than classical heat pump systems.
The drawback to the prior art of classical heat pumps is the high complexity, due to a large number of components, associated with high costs and a low efficiency at low outside temperatures.
The drawback to compact air conditioning systems is a substantially different vehicle architecture on account of their use, which prevents an application in conventional vehicles.